The U.S. Pat. No. 4,958,715 discloses a transport system comprising multiple pairs of belts disposed to allow a directional change along a transport path.
A problem encountered in such transport systems for validators is related to the construction of the frame of the validator. Said frame is usually made of at least one base plate, on which axes are secured perpendicularly for support of pulleys, the document-carrying belts being supported, and sometimes driven, by said pulleys. One advantage of a single base plate is to provide easy access for validator maintenance and belt replacement; however, the higher cost involved due to the larger diameters of axes that are necessary for this type of construction have led most manufacturers to prefer a frame construction comprising two parallel plates, each plate supporting one end of each axes. This type of two-plate construction allows to use thinner, cheaper rods for axes; however, maintenance is complicated because, if for example a belt has to be replaced, the operator has to completely dismantle a plate, usually the one that is closer to the belt that needs to be changed, remove the belts that are between the removed plate and the belt that has to be replaced, replace the belt and then reverse operations to finally reinstall the plate.
In modern validators, processing of the document comprises several steps, comprising e.g. identifying and authenticating the document by magnetic and/or optical means, rotating the document around a is plurality of axes for subsequent stacking in a predetermined orientation, sorting the document, and punching it out of the belt path into a stack. As a result, the validators are now made of a plurality of sub-parts, each of these being in charge of one of the above-mentioned functions. A single transport system carrying the document through all sub-systems is not easy to maintain; as a result, the problem of serviceability maybe solved by increasing the number of transport systems, hereafter called sub-systems, along the transport path, e.g. allocating one transport sub-system to each sub-part performing a function in the validator. This allows the use of shorter belts, being driven and supported by a smaller number of pulleys, rotating around a smaller number of axles.